1. Field of the Invention
This invention relates to an internal trim member for sound insulation in an inside of an automobile. More particularly it relates to an internal trim member for automobile useful as a sound proof material disposed on a partition wall between an engine room and a cabin or between a floor panel and a carpet.
2. Related Art Statement
In order to reduce the noise level inside the car, it has been particularly attempted to apply a sound proof material called an insulator onto a partition wall (dash panel) between an engine room and a cabin, between a floor panel and a carpet and the like among panels constituting a vehicle body.
FIG. 2 shows an example of a structure of an internal trim member suitable as an insulator disposed on the dash panel (dash insulator) or an insulator disposed on the floor panel (floor insulator).
In FIG. 2, a dash panel structure 38 inclusive of a dash insulator 36 is formed on a partition wall (dash panel) 34 between an engine room 30 and a cabin (chamber) 32, while a floor structure 46 inclusive of a floor insulator 44 is formed between a floor panel 40 and a carpet 64.
The dash panel structure 38 is formed by joining a constrained damping member 52 comprised of a laminate of an asphalt series damping material 48 and a constraining plate 50 onto an inner face of the dash panel 34 made from a steel plate and then joining the dash insulator 36 comprised of a laminate of a porous layer 54 and a sheet-like sound insulating layer 56 thereonto.
On the other hand, the floor structure 46 is formed by joining an asphalt series damping material 58 onto an inner face of the floor panel 40 made from a steel plate and then joining the floor insulator 44 comprised of a laminate of a porous layer 60 and a sheet-like sound insulating material 62 thereonto. A carpet 64 is arranged inside the floor structure 46.
The porous layers 54 and 60 acting as a sound proof layer are made from a felt using a powdery thermosetting resin as a binder, or a foamed body such as flexible urethane foam or the like. The sheet-like sound insulating layers 56 and 62 laminated on the porous layers 54 and 60 are made, for example, from a flexible polyvinyl chloride or an ethylene-vinyl acetate copolymer.
In the conventional dash insulator 36 or floor insulator 44, however, since the porous layers 54 and 60 are made from a flat plate-like material, they can not sufficiently be adhered to the surface of the body panel shaped into a complicated uneven form for increasing the strength or the like such as dash panel 34, floor panel 40 or the like, so that a space is formed and consequently the sound proof performances are frequently insufficient.
Furthermore, since the porous layer is not closely adhered to the body panel, the appearance inside the car is damaged. Moreover, the size accuracy is poor, so that there is caused an inconvenience in the attachment of other parts.
Recently, it has been proposed to use a urethane foamed body molded so as to match with the uneven form of the body panel, a compression shaped body of felt having a density of not less than 0.04 g/cm.sup.3 or the like instead of the flat plate-like porous layer as an internal trim member for automobile.
In such a urethane foamed body, however, a skin layer is formed in the surface or the cell membranes remain in the internal fine pore structure, so that air inside the foamed body is hardly moved to make the porous layer hard. Consequently, the sound insulating effect is insufficient.
In the felt compression shaped body, the felt is not less than 0.04 g/cm.sup.3, so that the body is locally hardened due to the presence of highly compressed portion, whereby the sound insulating performances are degraded and also the weight of the body as a whole becomes heave which conflict with the general goal of weight reduction of the automobile.